Proficiency Exam Flashcards
What is the simplest form of monosaccharide?
triose
What are the two trioses? Differentiate.
Glyceraldehyde - simplest aldose
Dihydroxyacetone - simplest ketone
What forms upon the reaction of an aldehyde with an alcohol? Draw and explain the mechanism.
A hemiacetal.
1.) The electrophilic oxygen in the alcohol group attacks the electrophilic carbonyl carbon.
2.) Upon the nucleophilic attack of the carbonyl carbon, electrons from the pi bond move towards the oxygen, and will form a negative charge.
3) The oxygen from the R-OH that attached to the carbonyl will have a positive charge.
4.) The intermediate is formed (which is unstable since there are negative and positive charges in the molecule).
5.) There will be a proton transfer (from the positively charged O to the negatively charged O).
6.) The hemiacetal is now formed.
A six-membered ring is called?
pyranose
a five-membered ring is called?
furanose
Cyclization from C1 to C5 of an aldohexose or C1 to C4 of an aldopentose forms a?
Cyclic hemiacetal
The monosaccharides can undergo interconversion between alpha and beta forms, using the open-chin structure as an intermediate. What is the process called? What do you call the enzymes that catalyze the reaction?
Mutarotation; Mutarotases
Sketch the Fischer and Haworth projections (pyranose and furanose form) of the following compounds:
D-xylose
D-arabinose
D-glucose
D-psicose
Answer on paper
What is the relationship of D-gulose and D-glucose in terms of stereochemistry?
diastereomers
[You can memorize the aldohexoses by hand]. Give all the C2 epimers.
D-Allose and D-Altrose
D-glucose an D-mannose
D-gulose and D-idose
D-galactose an D-talose
True or False. Only the furanose form is possible for ketopentoses.
True
Cyclization using C2 to C5 results into?
Hemiketal formation
In the conversion of Fischer projection to Haworth projection, what becomes the anomeric carbon?
The C1
Differentiate the alpha and beta anomers?
beta = cis
alpha = trans
Differentiate the configurational isomers
Enantiomers = nonsuperimposable mirror images
Diastereomers = nonsuperimposable, non-mirror images of one another
Anomers = stereoisomers that differ in the configuration at the anomric carbon
Epimers = stereoisomers that differ in the configuration at one carbon OTHER than the anomeric carbon
The resulting product when an aldose is oxidized using a mild oxidizing agent. What is being oxidized?
Aldonic acid, carbonyl carbon
The resulting product when an aldose is being oxidized using a strong oxidizing agent? What is being oxidized?
Aldaric aicid, C1 and C6
What is the product if an aldose is being oxidized at C6 via enzyme catalyzed reaction?
Alduronic (Uronic) Acid
Reduction of the carbonyl group on the sugar gives rise to the class of polyhydroxycompounds called ____?
Alditols
Elimination of water between the anomeric hydroxyl of a cyclic monosaccharide and the hydroxyl group of another compound yields to the formation of:
O-glycoside
What is sucrose?
The final product of photosynthesis, used as a primary energy source in many organisms. It is a disaccharide made up of alpha-glucose that is glycosidically linked to beta-fructose via alpha 1-2 glycosidic bond
A major animal energy source that is connecte via beta (1>4) glycosidic bond between glucose and galactose
Lactose
A major circulatory sugar in insects; use for energy. It is conneected via alpha (1>1) glycosidic bond between glucose and glucose
alpha-alpha trehalose
The dimer derived from the starch and glycogen polymers. It is an alpha (1>4) glycosidic bond between two units of glucose
maltose
The dimer of a cellulose polymer. It is connected via beta (1>4) glycosidic bond between two glucose units
cellobiose
A constituent of plant glycosides and some polysaccharides. It is connected via beta (1>6) glycosidic bond between two units of glucose
gentiobiose
What are homopolysaccharides?
a polysaccharide that contains only one kind of monosaccharide.
What are heteropolysaccharides?
A polysaccharide that is made up of several monosaccharides
what are the storage molecules?
starch and glycogen
what are the storage polysaccharides?
amylose and amylopectin
difference between starch and glycogen
starch = energy storage in plants
glycogen = energy storage in animals
differentiate the structure of amylose and amylopectin
amylose = continuous, unbranched chains of up to 4000 alpha D-glucose units joined by alpha (1>4) glycosidic bonds
amylopectin = highly branched polymer consisting of 2430 units of D-glucose joined by alpha (1>4) glycosidic bonds and branches created by alpha (1>6) glycosidic bonds
explain the structure of glycogen
-it constitutes up to 10% of liver mass and 1-2% of muscle mass
-alpha (1>6) branches for every 8-12 residues
-gives red-violet color with iodine
Draw the structure of galacturonic acid
.
When an aldose is being oxidized using a mild oxidizing agent, the carbonyl carbon becomes a COOH, leading to the formation of aldonic acid. Aldonic acid is said to have an equilibrium with?
Lactones (cyclic carboxylic esters)
Why is it that humans, even if they are starving, cannot utilize enormous quantities of glucose in the form of cellulose (i.e., why can’t humans gain energy if they eat plants?)
Because humans do not have enzymes that can catalyze the cleavage between the beta-(1>4)-glycosidic linkage
What are the structural molecules
Chitin and cellulose0
It is the major structural component of the exoskeletons of invertebrates, such as insects, crustaceans, and also occurs on the cell walls of fungi, algae, and yeasts. It is joined by beta-(1>4) glycosidic bond of N-acetyl-beta-D-glucosamine
chitin
These sugars are formed by mild reduction of sugars
sugar alcohols
Formerly called as mucopolysaccharides
glycosaminoglycans
Chondroitin sulfates, keratan sulfates of connective tissues, dermatan sulfates of skin, and hyaluronic acid are polymers of repeating disaccharide units of?
N-acetylgalactosamine
Draw the structure of beta-D-galactosamine
.
These are monosaccharides with one or more hydroxyl groups replaced by hydrogens
Deoxy sugars
The ribose moeity of nucleotides such as ATP and GTP is phosphorylated at what position
5’ position
an enzyme that catalyzes the hydrolysis of alpha-(1>4)-glycosidic bonds
amylases
an exoglycosidase and cleaves the alpha-(1>4) linkages from the nonreducing end of the polymer
beta-amylase
an endoglycosidase and hydrolyzes the alpha-(1>4)-glycosidic linkages along the chain to produce glucose and maltose
alpha-amylase
catalyze the hydrolysis of alpha-(1>6)-glycosidic bonds
debranching enzymes
Formed by bacteria that are components of dental plaque
dextrans
These are found in cell walls of nearly all plants. It is the major structural component of plants, especially wood and fibers.
-most abundant natural polymer
cellulose
almost a pure cellulose
cotton
Explain the structure of cellulose
-a linear polymer of approximately 2800 D-glucose units per molecule joined by beta-(1>4)-glycosidic bonds
-fully extended conformation with alternating 180 deg flips of glucose units
A polymer of D-galacturonic acid joined by alpha-(1>4)-glycosidic bonds
Pectin
These are polysaccharides based on a repeating disaccharide unit where one of the monomers is an amino sugar and the other has a negative charge due to a sulfate or carboxylate group
glycosaminoglycans
a natural coagulant that has a structure of D-glucuronic acid-2-alpha-(1-4)-N-sulfo-D-glucosamine-6-sulfate
heparin
a component of vitreous humor of the eye and the lubricating fluid of joints and has a structure of D-glucuronic acid-beta(1>3)-N-acetyl-D-glucosamine
hyaluronic acid
components of tendons, cartilage, and other connective tissues
chondroitin sulfate and keratan sulfate
Component of the extracellular matrix of skin
dermatan sulfate
structure of heparin
D-glucuronic acid-2-sulfate-alpha-(1>4)-N-sulfo-D-glucosamine-6-sulfate
structure of hyaluronic acid
D-glucuronic acid-beta-(1>3)-N-acetyl-D-glucosamine
structure of chondroitin sulfate
D-glucuronic acid-beta-(1>3)-N-acetyl-D-galactosamine-4-sulfate
structure of keratan sulfate
D-galactose-beta-(1>4)-N-acetyl-D-glucosamine-6-sulfate
these contain carbohydrate units covalently bonded to a polypeptide chain
glycoproteins
